The accompanying table gives summary data on cube compressive strength (N/mm2) f

Question

The accompanying table gives summary data on cube compressive strength (N/mm2) for concrete specimens made with a pulverized fuel-ash mix Sample Sample Sample Age (days) Size 67 71 Mean 25.95 34.71 SD 4.88 6.48 28 Calculate a 99% CI for the difference between true average 7-day strength and true average 28-day strength. (Use Ho : 7-128-0. Round your answers to two decimal places N/mm Interpret your 99% CI with 99% confidence, that the true difference falls outside these values with 99% confidence, we can say that the true difference falls between these values With 99% confidence, that the true difference falls above the upper bound with 99% confidence, that the true difference falls below the lower bound You may need to use the appropriate table in the Appendix of Tables to answer this question.

Explanation / Answer

##By using Minitab

Two-Sample T-Test and CI

Sample N Mean StDev SE Mean
1 67 25.95 4.88 0.60
2 71 34.71 6.48 0.77

Difference = mu (1) - mu (2)
Estimate for difference: -8.76000
99% CI for difference: (-11.30405, -6.21595)
T-Test of difference = 0 (vs not =): T-Value = -9.00 P-Value = 0.000 DF = 129

The 99% Confidence interval is given by

(-11.30405, -6.21595) N/mm^2

With 99% confidence we can say that the true difference falls between these values.

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